I've looked around, googled, etc. but I find no info on this. I'm going to adapt a Momo steering wheel from a race car i'm disassembling and mount it to the G25 base using an aluminum adapter i'm making. It's fairly simple, unscrew the 6 mounting screws, unplug the two wheel mounted push buttons from the circuit board (easily accessible when the wheel is off), Screw the aluminum plate tot he G25 assembly, screw the Momo wheel to the plate. Done! This gives me the same wheel size as is in my race car (13.5"). A much better, more realistic feel... Has anyone done this? You lose the function of the two buttons but I couldn't care less about that.

You can pretty much adapt any wheel to the G25. I got this one from Jegs for $100.00.
I bought a couple of buttons but haven't installed them yet.